This invention relates to an electric vehicle having left and right electric motors driving left and right driven wheels.
xe2x80x9cUtility machinexe2x80x9d is a term which refers generally to dollies used for loading and unloading; cultivators and tractors used in farming; mowers for cutting grass; and snow-removers and soon. Among utility machines there are electric vehicles propelled by electric motors. An electric vehicle of this kind is referred to in Japanese Patent Laid-Open Publication No.SHO-50-107619, xe2x80x9cSteering Control Apparatus of Electric Dollyxe2x80x9d. This electric dolly is shown in FIG. 27 hereof.
In FIG. 27, left and right electric motors (not shown) of an electric dolly 200 drive left and right driven wheels 201L, 201R to propel the electric dolly 200 along a path 202. When while the electric dolly 200 is traveling it deviates from the path 202 and a left side sensor 204L touches a left side slope 203L, the right side electric motor reverse-rotates to change the direction of the electric dolly 200 so that it returns to the path 202.
When the electric dolly 200 deviates from the path 202 and a right side sensor 204R touches a right side slope 203R, the left side electric motor reverse-rotates to change the direction of the electric dolly 200 so that it returns to the path 202.
However, because the electric dolly 200 starts to change direction only after one of the left and right sensors 204L, 204R has made contact with the respective slope 203L or 203R, it deviates relatively far from the path 202 before changing direction. Consequently, the electric dolly 200 snakes as it travels.
This snaking can be prevented by the driver changing the direction of the electric dolly 200 before either of the left and right sensors 204L, 204R touches the respective slope 203L or 203R. However, for the driver to change the direction of the electric dolly 200 without relying on the left and right sensors 204L and 204R, it is necessary for the driver to grip an operating handle 205 strongly and turn the electric dolly 200 with great force.
Changing the direction of the electric dolly 200 without relying on the left and right sensors 204L and 204R like this puts a large burden on the driver.
Also, when the driver changes the direction of the electric dolly 200 by force, the electric dolly 200 becomes unsteady and difficult to keep in a good traveling attitude.
To overcome this, electric vehicles having left and right electric motors driving left and right driven wheels and left and right brakes for adjusting the speeds of the left and right driven wheels have been proposed, as for example in Japanese Patent Publication No. SHO-48-4260, xe2x80x9cDirection and Propulsion Control Apparatus of Electric Carxe2x80x9d. With this electric car, transit control is possible whereby when an operating lever is pushed forward the car accelerates; when the operating lever is pulled backward the car is braked or reverses; when the operating lever is pushed to the left the right rear wheel accelerates but the left rear wheel is braked or reverses; and when the operating lever is pushed to the right the left rear wheel accelerates but the right rear wheel is braked or reverses. This transit control is carried out by the operating lever being operated to directly alter the settings of multiple potentiometers and thereby control respective electric currents supplied to the left and right electric motors.
However, in this case, the supplies of power to the left and right electric motors are altered in correspondence with the angle of inclination of the operating lever, essentially irrespective of the speed of the vehicle. And consequently, for example with an electric dolly, although there is no problem when the speed of the dolly is low, if the operating lever is operated when the speed is high, the dolly is liable to turn excessively due to inertial force.
Another electric vehicle having left and right electric motors driving left and right driven wheels appears in for example Japanese Patent Publication No. SHO-57-43003, xe2x80x9cMotor Control Apparatus of Electric Carxe2x80x9d. In an electric vehicle having a driving motor for each of a pair of wheels, this control apparatus inputs speed detection signals from speed detectors provided on each motor to a differential amplifier, and on the basis of this differential output controls the speed of one of the motors in correspondence with speed fluctuations of the other motor.
When the electric vehicle hits an irregularity in the road surface or a slope, the speed of one of the wheels may drop. When this happens without correction, the electric vehicle turns to the right or the left instead of moving straight forward, which is undesirable. To avoid this, with the control apparatus mentioned above, the speeds of the left and right wheels are matched, and consequently the electric vehicle does not turn on its own as a result of the state of the road surface.
In the above-mentioned Japanese Patent Publication No. SHO-57-43003, it is explained that when the operating shaft is tilted to the left or the right a speed difference between the left and right electric motors is generated and the electric vehicle turns to the left or the right. But in this case, it is difficult to distinguish whether the cause of a speed difference arising between the left and right wheels is an external one originating in the condition of the road surface or a human-initiated one (the operating shaft being operated). To make this distinction an electronic distinguishing circuit is needed, and electronic distinguishing circuits of this kind are complicated and costly, and even then the reliability of their distinguishing is not said to be high.
An invention relating to a rotary snow-clearing vehicle is disclosed in Japanese Patent Laid-Open Publication No. SHO-51-137214, xe2x80x9cControl Method of Rotary Snow-Clearing Vehicle having Automatic Speed Control Apparatusxe2x80x9d. In this control method, which is suitable for a rotary snow-clearing vehicle which travels on rails, the load on an engine for clearing snow is detected with a sensor, and the transit speed of the rotary snow-clearing vehicle is controlled on the basis of this detection signal. In the case of a rotary snow-clearing vehicle which simply moves forward or backward along rails, there is no problem; but with a snow-clearing machine for clearing snow from an ordinary road, because the vehicle body rocks to the left and the right under the action of the road surface and snow, the driver must constantly control the vehicle to the forward direction. Consequently, with a snow-clearing machine for ordinary roads, the control method mentioned above cannot be employed.
It is therefore an object of the present invention to provide an electric vehicle with which it is possible to make direction adjustments and turns of the electric vehicle without putting a burden on the driver and it is possible to make direction adjustments and turns with the electric vehicle in a stable state.
To achieve this object and other objects, a first aspect of the invention provides an electric vehicle having: a vehicle body; a left electric motor, mounted on the vehicle body, for driving a left driven wheel; a left brake, mounted on the vehicle body, for braking the left driven wheel; a right electric motor, mounted on the vehicle body, for driving a right driven wheel; a right brake, mounted on the vehicle body, for braking the right driven wheel; left and right control handles extending rearward from the vehicle body; left and right grips provided at the ends of the control handles; a left speed control lever, provided alongside the left grip, for controlling the left electric motor and the left brake; and a right speed control lever, provided alongside the right grip, for controlling the right electric motor and the right brake.
Left and right speed control levers are provided alongside left and right grips, and a left brake and electric motor are controlled with the left speed control lever and a right brake and electric motor are controlled with the right speed control lever. Consequently, because a driver can operate the left and right speed control levers while holding the left and right grips, the driver can make direction adjustments and turns of the vehicle with the left and right speed control levers while keeping the vehicle in a good attitude with the left and right grips. Also, because the driver can operate the left and right speed control levers while holding the left and right grips, the driver can easily operate the left and right speed control levers just with the fingers, without moving either hand. Consequently, the driver can operate the left and right speed control levers with a natural operating feeling (with an easy action).
An electric vehicle according to this first aspect of the invention also has a control unit for controlling the left and right electric motors. This control unit reads in the positions of an accelerator lever and the left and right speed control levers as an accelerator angle and a left brake angle and a right brake angle and converts the accelerator angle, the left brake angle and the right brake angle into an accelerator percentage, a left brake percentage and a right brake percentage and obtains a corrected left brake percentage by adjusting the left brake percentage for the influence of the right brake percentage and by correcting the accelerator percentage with this corrected left brake percentage obtains a left motor control value and controls the left electric motor with this left motor control value and obtains a corrected right brake percentage by adjusting the right brake percentage for the influence of the left brake percentage and obtains a right motor control value by correcting the accelerator percentage with this corrected right brake percentage and controls the right electric motor with this right motor control value.
Normally, the electric motors are controlled directly on the basis of the accelerator angle. However, with this first aspect of the invention, control is implemented wherein for example in control of the left electric motor, when the left brake angle is large the left electric motor control value is lowered, and when the right brake angle is large this is also taken into account and the left motor control value is lowered further. And the same control is carried out for the right electric motor. As a result, the waste of rotating an electric motor at a high speed while applying a brake is avoided. Also, whereas ordinarily it sometimes happens that the vehicle shakes due to an unbalance between the left and right electric motors, according to this first aspect of the invention, because for example with respect to the left electric motor not only the left brake angle but also the right brake angle is taken into account, there is no risk of this happening, and irrespective of the state of the travel surface, speed adjustment is made easy and the vehicle can move smoothly.
This electric vehicle may be a snow-clearing machine having a utility tool with an auger for displacing snow and a blower for blowing out displaced snow. In a snow-clearing machine, the state of loads acting on the utility tool is complex. However, by controlling the orientation of the snow-clearing machine by controlling the left and right driving wheels in accordance with the invention, this problem can be overcome and the auger and blower protected and efficient snow-clearing carried out.
A second aspect of the invention provides a transit control method for an electric vehicle having left and right electric motors for driving left and right driven wheels and having left and right brakes for adjusting the speeds of the left and right driven wheels, the method including the steps of: substituting the positions of an accelerator lever and left and right speed control levers controlled by an operator as an accelerator angle, a left brake angle and a right brake angle; converting the accelerator angle, the left brake angle and the right brake angle into an accelerator percentage, a left brake percentage and a right brake percentage; obtaining a corrected left brake percentage by adjusting the left brake percentage for the influence of the right brake percentage, obtaining a left motor control value by correcting the accelerator percentage with the corrected left brake percentage, and controlling the left electric motor with the left motor control value; and obtaining a corrected right brake percentage by adjusting the right brake percentage for the influence of the left brake percentage, obtaining a right motor control value by correcting the accelerator percentage with the corrected right brake percentage, and controlling the right electric motor with the right motor control value.
This electric vehicle may further have a utility tool, an engine for driving the utility tool and a clutch provided in a power transmission path from the engine to the utility tool, and in this case, preferably, the left motor control value is obtained by multiplying a value reached by correcting the accelerator percentage with the corrected left brake percentage by a correction coefficient less than one set in correspondence with a reduction in the speed of the engine occurring when the clutch is ON, and the right motor control value is obtained by multiplying a value reached by correcting the accelerator percentage with the corrected right brake percentage by a correction coefficient less than one set in correspondence with a reduction in the speed of the engine occurring when the clutch is ON.
When a large load acts on the utility tool, the speed of the engine falls sharply. When this happens, the outputs of the left and right electric motors are lowered and the transit speed of the machine is reduced. That is, the speed of transit of the vehicle can be made to correspond to the load on the utility tool; stopping of transiting of the utility machine due to an excessive load can be prevented; and because the work being carried out by the utility tool is interrupted less often, an improvement in the efficiency of that work can be achieved. Also, because the load acting on the utility part can be reduced, damage to the utility part can be suppressed and an increase in the life of the utility part can be achieved.
In a control method according to this second aspect of the invention, preferably, when the left and right brake angles are essentially the same, the speeds of the left and right electric motors are read in and the speed of the whichever of the left and right electric motors is at the higher speed is controlled to the speed of the electric motor at the lower speed. That is, in straight-forward running, only when the left and right brake angles are essentially the same, control is carried out to match the speeds of the left and right electric motors. By this means it is possible to raise the straight-forward characteristic of the vehicle without being affected by the path condition. And because it is the higher speed that is adjusted to match the lower speed, when one of the driving wheels has mounted an irregularity in the path surface or a slope, the speed of the vehicle is lowered and stabilizing the vehicle body is made easier.
Also, in a control method according to this second aspect of the invention, preferably, when the accelerator percentage is written ACC %, the left brake percentage is written BKL %, the right brake percentage is written BKR %, a coefficient of influence on whichever of the left and right electric motors is being considered of the brake percentage pertaining to the other electric motor is written p (where p less than 1), and the maximum value of the control value of each electric motor is written Vmax, then the corrected left brake percentage is calculated as (BKL %+pxc3x97BKR %xc3x97ACC %), the left motor control value TG2L is calculated as Vmaxxc3x97ACC %xc3x97{1xe2x88x92(BKL %+pxc3x97BKR %xc3x97ACC %)}, the corrected right brake percentage is calculated as (BKR %+pxc3x97BKL %xc3x97ACC %), and the right motor control value TG2R is calculated as Vmaxxc3x97ACC %xc3x97{1xe2x88x92(BKR %+pxc3x97BKL %xc3x97ACC %)}. In this way, the accelerator percentage ACC % is taken into account in obtaining the corrected left brake percentage (BKL %+pxc3x97BKR %xc3x97ACC %). By weakening the influence of the right brake percentage BKR % on the left motor control value when the accelerator percentage ACC %, which is linked to the vehicle speed, is small, and strengthening it when the accelerator percentage ACC % is large, a left motor control value TG2L corresponding to the vehicle speed is set. And the same applies to the right motor control value TG2R.
Also, in a control method according to this second aspect of the invention, when the electric vehicle further has a utility tool and an engine for driving the utility tool and a clutch disposed in a power transmission path from the engine to the utility tool, the left and right electric motors are preferably controlled in accordance with a detected load on the engine. Specifically, for example, the left motor control value is obtained by multiplying a value reached by correcting the accelerator percentage with the corrected left brake percentage by a correction coefficient less than one set in correspondence with a reduction in the intake negative pressure of the engine occurring when the clutch is ON, and the right motor control value is obtained by multiplying a value reached by correcting the accelerator percentage with the corrected right brake percentage by a correction coefficient less than one set in correspondence with a reduction in the intake negative pressure of the engine occurring when the clutch is ON. That is, when the engine encounters a large load, the intake negative pressure of the engine rises. And at this time, control is executed to lower the outputs of the left and right electric motors and reduce the transit speed of the electric vehicle.